An elliptical headlamp conventionally comprises a light source such as an incandescent filament or the luminescent arc of a discharge lamp, this source being located in a first focal region of a mirror so that the light reflected by it is directed towards a second focal region situated in front of the first one. A lens, generally plano-convex, is focused on this second focal region, so as to project the light spot formed in said second focal region onto the road.
This light spot can be modeled, for example with a mask, to form a beam with cut-off as required, such as a dipped beam, an upper edge of this mask defining the profile of this cut-off.
Because of this possibility of forming a sharp cut-off, and because of the excellent recovery by the mirror of the light flux emitted by the source, such headlamps have been used successfully for many years to form dipped European beams with cut-off in a “V” shape.
To form the main beam, it is usual to provide another headlamp, dedicated to this function and generally including a parabolic mirror focused on another source. Headlamps of the elliptical type are in fact somewhat unsuitable for producing a main beam, since it can be difficult, in the axis of the road, to obtain the illumination minima required by the regulations or the technical specifications. In particular, the beam formed by a headlamp of the elliptical type exhibits fairly regular brightness, with no marked point of concentration at its center, and a complex contour particularly with substantial overthickness towards the top and towards the bottom in terms of the optical axis, which has the drawback of illuminating the road too close to the vehicle. In contrast, a parabolic mirror makes it possible to have an extremely large amount of light available in the axis and just below it.
Hence a vehicle equipped with elliptical dipped headlamps possesses separate, dedicated main-beam headlamps, which naturally increases the manufacturing cost of the set of headlights and their size on the front of the vehicle. In particular, the necessity to provide dipped and main-beam headlamps with fundamentally different principles means that recourse is had to designs and to sets of tools (moulds, presses, etc.) which are completely specific, which contributes to this high overall manufacturing cost. Moreover, when it is turned off, the external appearance of an elliptical headlamp is very different from that of a parabolic headlamp, which can impair the aesthetics of the frontal region of the vehicle.